In FIG. 6 a block diagram of a typical trunked communication system is shown. The radios or subscriber units 200 which are part of system 600 communicate over control channel 602 with the system central controller 604 in order to receive status and control information from the central controller 604. The system central controller 604 acts as the system coordinator and is responsible for assigning radios 200 to different repeaters 606 (channels) so that they may communicate amongst each other. The central controller 604 is also responsible for knowing where each of the radios are located (i.e. what voice channel) and for controlling other features typically found in a modern trunked communication system (e.g. handling phone patches, coordinating groups of radios in emergency situations, etc.). The typical central controller 604 includes a main processing unit such as a computer with appropriate control software which controls the operation of controller 604. Also normally included as part of controller 604 is a video display and keyboard in order to allow the central control operator to communicate with the system. The signals which are sent from the central controller 604 to the subscriber units 200 over the control channel 602 are typically called outbound signaling words ("OSW's"). The control signals going from radios 200 to the central controller 604 are called inbound signaling words (ISW's). OSW's inform radios 200 when to change channels automatically so as to communicate with other members in the same radio talk group over an assigned voice channel 606 which has been assigned by the system central controller 604.
When requesting a channel 606 for a talk group call, the radio unit 200 sends in a single word group request (if affiliated) with its individual radio identification number. The central controller 604 generates a grant OSW for the talk group affiliated with the radio unit that transmitted the channel request by referencing a radio ID to talk group affiliation database residing in the central controller 604. If there is no talk group affiliation in the central controller database (e.g., due to corrupt data, etc.), the central 604 requests a dual word ISW from the radio unit which identifies the unit ID and the desired talk group. If the radio unit changes talk groups, or systems, it immediately begins to receive calls for the new talk group or system and preferably performs an auto affiliation sequence after being on the selected talk group for about 2 seconds.
If PTT is asserted before auto affiliation, the radio unit 200 sends in a dual word ISW identifying the unit's radio ID number and the new desired talk group affiliation. The central controller 604 will store the talk group information in the affiliation table and then if a voice channel 606 is available, it will generate a grant OSW for that talk group. The grant OSW is initially sent out as a dual word grant to identify the transmitting unit and the talk group number. The requesting radio 200 sees its individual and talk group IDs in the grant OSW and goes to the voice channel 606 as a transmitting radio. Any other subscriber units 200 which are currently operating in the same talk group also see the talk group ID in the grant OSW and move to the same voice channel 606 as receivers. After the dual OSW grant is sent out 4 times, subsequent assignment update OSWs are transmitted by the central controller 604 as single word OSWs with simply the talk group ID and the voice channel it is assigned to the particular talk group.
An example of a typical trunked conversation will begin by one radio 200 in group "A" pressing PTT which automatically sends an ISW over the control channel 602 to the central controller 604 requesting a voice channel 606 grant. Once the request comes in, central controller 604 decides which voice channel 606 to assign and transmits an OSW via control channel 402 back to the radios 200. The OSW will inform all radios 200 in group "A" to move to repeater No. 2 for example, at which point all the radios in group "A" will move to that repeater to begin their conversation. Some trunked radio communication systems do not use a central control channel, but embed the control information within the voice channels such as by sending the control information using low-speed data which does not affect the voice communication.
There is currently no way for more than two radio users in a trunked radio communication system to establish communications with one another and not be heard by all members of a radio talk group or announcement group in a trunked radio system. The presently available feature of "Group Regrouping" (also known as patching) is initiated by an operator at the fixed-end of the radio communication system in order to let all members of two or more separate radio talk groups to communicate with each other.
Another feature found in trunked radio systems called "Dynamic Regrouping" is a means by which an operator at the fixed-end can group two or more users together, typically in an emergency situation, and later cancels the regrouping when the radio users no longer need to communicate with each other (i.e., after the emergency situation has terminated). A current "Regroup Request" feature allows users to request Dynamic Regrouping, but the fixed-end operator is still required to perform the regrouping. Also, a special zone/channel position must be reserved for Dynamic Regrouping operation on each of the trunked systems the radio is able to operate in.
Finally, another feature found in present trunked communication systems is called Private Conversation.TM. which allows one radio to establish a private conversation with a second radio. This feature however does not allow for more than two radios to communicate with each other, so group conversations can not be accomplished. Also, the feature does not allow for affiliation.
A need exists for a method by which radio users can select a talk group on their own so that a group of radio users can communicate with each other for a certain period of time, without other users in the system participating in the conversation.